Subsea well workover system and method

ABSTRACT

A string of pipe is stored in a body of water for working over a subsea well. The string is stored in a substantially linear configuration having controlled curvatures along its length with radii that are not smaller than the minimum yielding radius of curvature of the pipe material. The string may be made up from individual segments of threaded pipe. One end of the string is inserted into the well using a pipe drive assembly connected with the wellhead. The opposite end of the string is connected to a line that extends to a surface facility. The string may be rested on the bottom of the sea or may be floated on the water surface or may be suspended with buoyancy devices in various orientations between the sea bottom and the water surface. The pipe string may be stored within a tubular sleeve or may be disposed directly in the seawater. When the pipe is substantially horizontally oriented, an arching guide is used to divert the working end of the string from its storage position to a substantially vertical position for insertion into the well. The drive and guide may be permanently associated with the well or may be portable for movement to another subsea well. The drive and guide may be mounted in a buoyancy-controlled assembly. A remotely operated vehicle (ROV) is used to assemble and move the guide, drive and pipe through the water.

BACKGROUND SETTING OF THE INVENTION

[0001] Subsea wells are usually serviced or worked over with the same type rig or ship used to drill and complete the well. These rigs are large and expensive, particularly when of the type required for wells in deep water.

[0002] The prior art has suggested techniques and equipment for working on subsea wells without the use of large rigs. One approach has been to use coiled tubing to work on the completed well. The coiled tubing can be deployed and used from a relatively small workboat that is substantially less expensive to operate than a conventional drilling or completion rig.

[0003] Suggested prior art systems for working on subsea wells have also included self-contained, watertight-coiled tubing assemblies that are lowered into the water and positioned at the wellhead of the subsea well. See U.S. Pat. Nos. 5,002,130 and 4,899,823. An injector drive assembly secured to the wellhead propels the coiled tubing into and out of the well. It has also been suggested to position the injector drive assembly and the coiled tubing directly into the water without first enclosing the components in a watertight container.

[0004] Coiled tubing provides a desirable work string for many simple workover applications in that it is a continuous string that can be stored in a compact coil. A derrick and makeup and handling tools normally required for use with a string of jointed pipe are not required when using a coiled tubing string.

[0005] Conventional coiled tubing made of metal, however, suffers from limitations imposed by the requirement to repeatedly straighten and re-bend the pipe while unspooling and spooling the pipe on its storage reel. As compared with jointed pipe of the same dimensions, coiled tubing is more expensive, shorter lived, limited in pressure handling capabilities and more susceptible to wear and corrosion. Deploying and reeling the coiled tubing also requires the use of a curving injector head to straighten the pipe during injection into the well and to bend the pipe as it is being extracted from the well and coiled back onto the reel.

SUMMARY OF THE INVENTION

[0006] A string of pipe formed from individual steel pipe joints secured together at their ends by threaded connectors is positioned and stored in or on the water in the vicinity of a subsea well. The pipe string can be as long as desired for use in deep and ultra-deep water. In the preferred form of the invention, the pipe sections are secured together with flush joint connections so that the resulting pipe string has a uniform outside diameter along most of its length.

[0007] The pipe string is formed as an elongate continuous length of pipe that extends away from, or about, the subsea well into the water area between the sea bottom and the water surface. The end of pipe to be inserted into the well is positioned adjacent the subsea well and the opposite end may be located several miles away.

[0008] The pipe may extend through the water in a linear, essentially non-curving configuration or may be curved in multiple, extended curving open loops or spiral or helical configurations. The radii of any curves imposed in the pipe string are maintained at values greater than the minimum-bending radius of the pipe. The pipe string is inserted into the subsea well to produce well fluids from the well, place or remove tools, open or close valves, work the well over, and process, inspect and/or perform any other required subsea or down-hole well activity.

[0009] During the initial introduction of the stored pipe into the subsea well, in one form of the invention, the end of the pipe to be inserted into the well is moved through a guide that redirects the pipe from its substantially horizontal water storage position to a substantially vertical position for introduction into the well. The radius of the curve of the guide is maintained large enough to prevent plastic deformation of the pipe. The guide may include gripping elements that engage the external surface of the pipe and propel the pipe for movement into and out of the well.

[0010] The non-inserted end of the pipe may be connected by a service line to a surface support facility such as a floating work vessel or a sea floor supported platform. The service line may be a flexible supply hose, a string of jointed pipe sections or other suitable, elongate, fluid-communicating tubular body. The service line may also include, or may alternatively comprise, an electric slickline, wireline or other equivalent connection.

[0011] The pipe string may be stored in open water or may be received within a storage sleeve. In one form of the invention, the storage sleeve is provided with a suitable corrosion inhibiting liquid or other treating material. Seals extending about the annulus between the pipe string and the storage sleeve retain the treating fluid within the sleeve as the pipe is moved into and out of the sleeve.

[0012] A work string constructed of individual steel pipe segments secured together with conventional end connectors is significantly less expensive than a coiled tubing string having similar internal dimensions. Storing the string of pipe in a configuration that does not require repeatedly yielding the pipe material reduces the likelihood of fatigue-induced failure in the string. The use of conventional jointed pipe also permits higher operating pressures than those possible with continuous coiled tubing.

[0013] While the preferred form of the invention employs individual sections of flush joint pipe to form a pipe string, the present invention anticipates the use of a string of unjointed pipe positioned in the water in a linear or curving configuration having curvatures with radii that are not less than the minimum non-yielding radius of curvature for the pipe.

[0014] In one broad aspect of the invention, axially extending “unyielded pipe” (that is, pipe that has not been bent in a curve having a radius smaller than the minimum allowable non-yielding bending radius of the pipe) is positioned with its central axis oriented in a direction that is not parallel to the central axis of a subsea well that is to be engaged by a string of pipe that includes the unyielded pipe. The unyielded pipe is moved along a curving path and then allowed to straighten to redirect the central axis of the unyielded pipe to an axially extending orientation substantially parallel with the axis of the subsea well. One end of the pipe string in this parallel orientation is inserted into the well and the pipe string is driven through the well with a propulsion device that is submerged in the body of water overlying the subsea well.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a vertical elevation, partially in section, illustrating a surface support facility working on a subsea well using a pipe string of the present invention;

[0016]FIG. 2 is a vertical elevation, partially in section, illustrating a modified form of the invention applying different type work strings of the present invention to a subsea well;

[0017]FIG. 3 is a vertical elevation, partly broken away, illustrating a surface support facility working over a subsea well using a submerged work string carried within a protective sleeve;

[0018]FIG. 3A is a vertical section, partially broken away, illustrating a sliding seal disposed between the work string and a protective sleeve to retain corrosion inhibiting fluid in the sleeve as the pipe is advanced through the sleeve;

[0019]FIG. 3B is a vertical section, partially broken away, illustrating a fixed seal at one end of the protective sleeve providing a sliding seal between a surface supply line and the pipe string of the present invention; and

[0020]FIG. 4 is a vertical elevation illustrating a modified form of the present invention storing the pipe string of the present invention in multiple curving open loops.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0021]FIG. 1 illustrates a support facility indicated as a surface vessel 11 on a surface S of a body of water W servicing a subsea well 12 at a distant underwater location on a water bottom 13. A pipe work string 14 extends at substantially a diagonal to the horizontal between the work vessel 11 and the well 12.

[0022] A controlled buoyancy guide head 16 is anchored above the well 12 with anchoring lines 17 that extend to the water bottom 13. The pipe string 14 extends through the guide 16 and through a pipe drive assembly head 20 secured to the top of the well 12. An ROV 25 is used to position and assemble the guide head 16 and drive assembly 20 over the well 12.

[0023] As thus illustrated in FIG. 1, it will be appreciated that the pipe string 14 includes a section of unyielded pipe 14 a having a central axis that extends diagonally in a substantially non-parallel direction relative to a substantially vertically oriented central axis 12 a of the subsea well 12. The pipe 14 a is reoriented from its non-parallel orientation to its parallel orientation as it passes through the buoyancy guide head 16. In this application, as well as the others illustrated herein, an unyielded pipe section is moved around a curving path such that the central pipe axis becomes parallel with the central axis of the subsea well. The curving path has a radius of curvature that is greater than the minimum allowable non-yielding bending radius of the pipe material in the curved section whereby the bent or curving pipe section is not yielded as a result of moving over the curving path.

[0024] The assembly 20 may be bolted to the wellhead or otherwise suitably secured relative to the wellhead so that the linear driving force exerted by the drive assembly 20 forces the pipe string 14 into the well 12. The drive assembly 20 may be enclosed within a protective housing or may be directly exposed to the seawater.

[0025] The buoyancy guide 16 may be constructed in any manner suitable for regulating the position of the guide in the water relative to the drive assembly 20. Positive flotation or surface controlled displacement mechanisms may be employed in the buoyancy head 16 to achieve the desired positioning of the head relative to the well 12. The lines 17 may be any suitable line, including flexible or rigid lines, that assist in maintaining the relative lateral placement of the buoyancy guide 16 and the well 12.

[0026] A supply line 26 extends between the surface vessel 11 and the well 12 to provide hydraulic power, electric power, and/or data and control signals as required to accomplish the desired workover procedure. The supply line 26 may be a conventional flexible line having one or many conduits or conductors. The supply line 26 may be used to supply the power required to operate the drive assembly 20 and to communicate with the ROV 25. Additionally, the supply line 26 may be used to work with the work string 14, circulate fluid or otherwise perform services required in the workover, production and/or servicing of the well 12.

[0027] A controlled buoyancy device 27 is used to support the pipe string 14. Multiple such controlled buoyancy devices may be deployed along the length of the pipe string 14 if necessary to maintain a desired orientation of the string in the open water. The buoyancy devices may also be tethered to the bottom 13 if desired.

[0028] A second work string 30 is illustrated extending from the vessel 11 along the surface S of the water body W. Buoyancy devices 31 support the string on the water surface S. A floating curving guide 32 directs the pipe string 30 vertically down into the water W toward the subsurface well 12. The lower end (working end) of the string is introduced through the guide 16 to the drive head 20 to insert the working end of the string into the well 12. The opposite end (topside end) of the string 30 is connected by a flexible line 33 supplied from a reel 34 to communicate hydraulic fluid or well fluid or working materials between the vessel 11 and the well 12.

[0029] As illustrated herein, it will be understood that an unyielded pipe section 30 a of the pipe string 30 is oriented in a direction that is not substantially parallel with the direction of the centerline 12 a of the subsea well 12. When the section 30 a is moved through the curving guide 32, the orientation of the central axis of the pipe section 30 a is changed to become substantially parallel with the central axis 12 a of the well.

[0030] The string 30 slides through the flotation devices 31 as it advances into the water W. The lateral positioning of the flotation devices 31 may be remotely controlled by signals sent from the vessel 11 causing the devices to selectively grip or release the pipe as it is being moved. The flotation devices 31 may also have remotely controlled, self-propulsion capabilities to move them along the length of the pipe 30 as required to assist in deploying and retrieving the pipe string.

[0031] A third work string 40 is illustrated resting on the bottom of the sea floor 13. The working end of the work string 40 passes through a curving guide 41 that is part of a controlled buoyancy assembly 42. A drive head assembly 43 is included with the controlled buoyancy assembly 42.

[0032] An operator in the vessel 11 remotely controls the buoyancy of the assembly 42 as the ROV 25 moves the assembly into position above the wellhead 12. The flexible line 26 may be connected to the controlled buoyancy assembly 42 to power and/or transfer fluids or information and/or otherwise communicate with the drive head assembly 43, the working end of the pipe string 40 and/or the well 12.

[0033]FIG. 2 illustrates a surface support vessel 50 assembling individual joints of pipe 51 and 52 into an elongate string 53 used to work over the well 12. The pipe is being assembled and fed from the ship 50 through a curving guide 55 that directs the pipe vertically down through the water W from the surface S. A work string 56 extends away from the vessel 50 where it is stored on the water surface S resting upon flotation devices 57. The working end of the string 53 is fed into the well through a drive head assembly 60 that is secured to the well 12. The drive head assembly 60 propels the string 53 into and out of the well as required to service, produce or otherwise deal with the well 12 and its contents.

[0034] The work string 56 may be drawn onto the vessel 50 and fed through the curving guide 55 to replace or supplement the string 53.

[0035] A second work string 61 is illustrated submerged below the surface S of the water body W. Controlled buoyancy devices 62 regulate the depth of the string 61 below the water surface. The string 61 slides through the flotation devices 62 as it is being run into or retracted from the well 12. A controlled flotation guide assembly 63 redirects the substantially horizontally disposed pipe string 61 to a vertical position for introduction into the well 12. A flexible supply line 65 provides support and communication for producing and servicing the well and operating the drive assembly 60. A flexible anchor line 66 is used to hold one or more of the flotation devices 62 fixed relative to the sea bottom 13.

[0036]FIG. 3 illustrates a surface vessel 70 having a flexible supply line 71 connected to the end of a work string 72 that extends through a protective sleeve 75. The internal diameter of the sleeve 75 is sufficiently large to accommodate the pipe string 72 with an additional annular space 76 between the sleeve and pipe string. A suitable corrosion inhibiting or other fluid is disposed within the annular area 76 to minimize corrosion or otherwise process or test the string 72.

[0037] The sleeve 75 is maintained at a desired location below the surface S of the water by suitable buoyancy devices 78. The sleeve 75 and enclosed work string 72 extend to the water body W in an elongate open loop that brings the working end of the work string back to a curving guide 80 positioned atop the subsea well 12. The guide 80 has a radius of curvature that is greater than the minimum radius of curvature below which the material of the pipe string 72 yields.

[0038] A pipe injection drive head 81 is secured to the well 12 for propelling the pipe string 72 into and out of the well. The drive head assembly 81 and guide 80 are supported over the well 12 by struts 85 that are secured to a baseplate 86 at the bottom of the well 12.

[0039] The assemblies 81 and 80 may be moved by a line deployed from the vessel 70 and secured to a lifting eye 87 to be moved from one subsea well to another. In performing this operation, it is only necessary to elevate the assembly sufficiently to clear projections from the sea bottom 13. An ROV is used in the positioning and deployment of the assembly.

[0040]FIG. 3A illustrates a sliding seal 90 formed internally of the sleeve 75. The seal 90 moves with the pipe 72 in the direction of an arrow 91 through the sleeve 75 as the drive head assembly 81 advances the pipe 72 into the well 12. The seal sliding through the inside of the sleeve 75 traps the corrosion inhibiting fluid in the annular area 76. As the pipe is advanced into the well 12, and the supply line 71 is pulled through the sleeve 75, the sliding seal 90 prevents egress of the treating fluid from the sleeve. The supply line 71 includes a line 91 used to supply fluid to the inside of the pipe string 72 and a return line 92 used to return displaced fluid in the area 76 back to the support vessel 70.

[0041]FIG. 3B illustrates a modified form of a seal 95 used to contain the treating fluid within the annulus 76 of the sleeve 75 as the pipe advances through the sleeve. The seal 95 is fixed relative to the sleeve 75 and maintains a sliding seal with the external surface of the supply line 71 as the line 71 follows the advancing work string 72 through the sleeve and to the subsea well 12. Fluid is supplied to the work string 72 through a conduit 96 and returned to the vessel through a return line 97.

[0042]FIG. 4 illustrates a modified form of storing and deploying the work strings of the present invention from a surface support vessel 100 at the surface S of the body of water W. A pipe string 101 extends in several open loops between free moving forming guides 102 and curving guides 103 and 104. The guides 102 are raised and lowered as the pipe is deployed or retracted relative to the well The working end of the string 101 is introduced into the well 12 in a manner previously described with reference to the string 14 and the buoyancy guide 16 of FIG. 1. The end of the pipe string at the support vessel 100 may be connected to pumps or other surface control or production devices or means required for working over, producing or otherwise dealing with the well 12.

[0043] The means and method for practicing the invention, and the best mode contemplated for practicing the invention, have been described herein. It is to be understood however, that the foregoing description is illustrative only, and that other means and methods as well as materials of construction may be employed in the practice of the present invention without departing from the scope of the invention. Additions, deletions and other modifications in the specifically described embodiments may be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the following appended claims. 

1. A method of extending a pipe string to a subsea well, comprising: orienting the central axis of an axially extending unyielded section of pipe in a direction such that the central pipe axis is not parallel to the central axis of a subsea well; moving the unyielded pipe section around a curving path such that the central pipe axis becomes parallel with the central axis of the subsea well, such curving path having a radius of curvature that is greater than the minimum allowable non-yielding bending radius of the pipe section whereby said pipe section is not yielded as a result of moving over said curving path; inserting one end of said pipe string into said subsea well; and propelling at least a portion of said pipe string through said subsea well with a propulsion mechanism submerged in a body of water that overlies said subsea well.
 2. A method as defined in claim 1, further comprising: communicating power and/or fluid and/or data between said subsea well and a surface facility at a surface of said body of water.
 3. A method as defined in claim 1, further comprising: servicing, working over or otherwise acting upon said subsea well with said pipe string.
 4. A method as defined in claim 1, further comprising: securing said propulsion mechanism to said subsea well.
 5. A method as defined in claim 1, further comprising: securing said propulsion mechanism to said subsea well with a remotely operated underwater vehicle.
 6. A method as defined in claim 1, further comprising: moving the unyielded pipe section around a curving path of at least 90 degrees.
 7. A method as defined in claim 1, further comprising moving the unyielded pipe section around more than one curving path of at least 90 degrees.
 8. A method as defined in claim 1, further comprising controlling the position of said pipe string in said body of water with the use of buoyancy devices.
 9. A method as defined in claim 1, further comprising providing a curved guide for bending said pipe section around said curving path.
 10. A method as defined in claim 9, further comprising supporting said curved guide on a flotation device.
 11. A method as defined in claim 1, further comprising placing said pipe string in a sleeve for isolating at least a part of said pipe string from the water in said body of water.
 12. A method of working on a subsea well, comprising: placing a linearly extending length of a metal pipe within and/or on a water body overlying said subsea well in a substantially non-vertical orientation, forming a bend in a portion of said linearly extending length of metal pipe within said body of water, below a surface of said body of water, without yielding said metal pipe in said bend, whereby a portion of said metal pipe is oriented substantially parallel to a central axis of a well pipe already installed in said subsea well, inserting said substantially parallel oriented length of metal pipe directly from said body of water adjacent said subsea well into said well pipe of said subsea well, and working on or in said well with the assistance of said extended length of metal pipe.
 13. A method as defined in claim 12, further comprising: communicating power and/or fluid and/or data between said subsea well and a surface facility at said surface of said body of water.
 14. A method as defined in claim 12, further comprising: servicing, working over or otherwise acting upon said subsea well with said pipe string.
 15. A method as defined in claim 12, further comprising: inserting said substantially parallel oriented length of pipe into said well pipe with a propulsion mechanism.
 16. A method as defined in claim 15, further comprising: securing said propulsion mechanism to said subsea well with a remotely operated underwater vehicle.
 17. A method as defined in claim 12, further comprising: forming said bend around a curving path of at least 90 degrees.
 18. A method as defined in claim 12, further comprising forming bends around more than one curving path of at least 90 with sections of linearly extending pipe positioned between said bends.
 19. A method as defined in claim 12 and bad, further comprising controlling the position of said pipe string in said body of water with the use of buoyancy devices.
 20. A method as defined in claim 12, further comprising providing a curved guide for bending said pipe section around said curving path.
 21. A method as defined in claim 20, further comprising supporting said curved guide on a flotation device.
 22. A method as defined in claim 12, further comprising placing said pipe string in a sleeve for isolating at least a part of said pipe string from the water in said body of water.
 23. A method of working on a subsea well with an elongate string of pipe, comprising: placing an axially extending, elongate string of pipe in or above a body of water overlying the subsea well, non-yieldingly bending a portion of the string of pipe from an orientation that is substantially non-parallel with the axis of the well to an orientation that is substantially parallel with the axis of the well, and extending the substantially parallel portion of the string of pipe into direct contact with the water body and through the water body directly into the subsea well.
 24. A method as defined in claim 23 further comprising securing together multiple lengths of tubular pipe sections to form said elongate string of pipe.
 25. A method as defined in claim 24 wherein said multiple lengths of tubular pipe sections have a flush joint connection whereby said elongate string of pipe has a substantially constant outside diameter along a major portion of its assembled length.
 26. A method as defined in claim 23 wherein at least a portion of said elongate string of pipe is supported in or above said water body with buoyancy devices.
 27. A method as defined in claim 23 wherein a submerged powered drive mechanism connected with the subsea well propels the parallel portion of the elongate string of pipe into the well.
 28. A method as defined in claim 27 wherein said powered drive mechanism is movable from one subsurface well location to another subsurface well location.
 29. A method as defined in claim 23 wherein a surface support facility connects through said elongate string of pipe to the subsea well.
 30. A method as defined in claim 23 wherein said elongate pipe string is bent at a location below the surface of the water body.
 31. A method as defined in claim 23 wherein said elongate pipe string is bent at a location above the surface of the water body.
 32. A method as defined in claim 24 wherein said elongate pipe string is bent at a location adjacent the subsea well.
 33. A method as defined in claim 23 wherein said elongate pipe string is bent through a change of direction of at least 90 degrees at multiple locations along its length and whereby each such bend is a non-yielding bend of the pipe string.
 34. A system for working on an underwater well, comprising: a surface support facility at the surface of a body of water overlying said underwater well, a pipe string connected between said surface support facility and said underwater well, said pipe string having a linearly extending first length that is substantially non-vertically disposed and a second linearly extending length that is substantially vertically disposed, said first length positioned intermediate said second length and said surface support facility, and a powered drive mechanism positioned between said first section and said underwater well for inserting said second length into said underwater well.
 35. A system as defined in claim 34, comprising: at least one bend in said pipe string between said first and second linearly extending lengths whereby the orientation of said linearly extending string changes from said substantially non-vertically disposed position to said substantially vertically disposed position, such bend having a radius of curvature that does not exceed the bending radius of curvature of the material of the pipe string that would cause yielding of the material of the pipe string.
 36. A system as defined in claim 35 wherein said bend occurs within the body of water.
 37. A system as defined in claim 35 wherein said bend occurs above the body of water.
 38. A system as defined in claim 34 wherein said powered drive mechanism is secured to said underwater well.
 39. A system as defined in claim 34 wherein said surface support facility provides fluids and/or power and/or communication between said surface support facility and said underwater well.
 40. A system as defined in claim 34 wherein controlled buoyancy devices are used to regulate the position of said pipe string within said body of water.
 41. A system as defined in claim 34 wherein said pipe string and said powered drive mechanism and said underwater well are equipped with connecting structures for engagement with and/or manipulation by a remotely operated underwater vehicle.
 42. A system as defined in claim 34 having a protective sleeve that prevents contact with at least a portion of said pipe string with the water within said body of water.
 43. A system defined in claim 34 wherein said first length of said pipe string is substantially horizontally disposed in or above said body of water.
 44. A system as defined in claim 34 wherein said pipe string has at least two bends along its length, such bends separated from each other by lengths of linearly extending pipe and providing a change in direction of at least 90 degrees and having a radius of curvature less than the minimum, non-yielding bending radius of the material of the pipe.
 45. A system as defined in claim 34 wherein the least a portion of said pipe string rests on the bottom of said body of water. 